It has often been noted that the output of oil or gas wells falls off more rapidly than one would attribute to reserve depletion. In other cases, wells drilled into known producing formations are found to have a production rate much below that which would be predicted from the information known about the reservoir.
Various treatments of such wells and the surrounding formation have been employed to improve hydrocarbon recovery. Commonly employed processes involve the injection of aqueous acidic solutions into the formation to dissolve portions of the formation and thus increase the permeability of the formation. Examples of such acidic aqueous solutions include aqueous solutions of hydrochloric acid, hydrofluoric acid, or mixtures of hydrochloric and hydrofluoric acid.
Another approach that has been employed in the past has involved the injection into the formation of an organic liquid having at least some solubility for both oil and water either alone or in combination with aqueous acid. Some typical examples of such techniques are disclosed in U.S. Pat. No. 2,356,205 (Blair, et al.); U.S. Pat. No. 3,402,770 (Messenger); U.S. Pat. No. 3,548,945 (Gidley); U.S. Pat. No. 3,819,520 (Jones, et al.); and U.S. Pat. No. 3,915,233 (Slusser), the disclosures of which are incorporated herein by reference.
In general it is desirable for the organic liquid well treating agent to be a material having miscibility with both active and spent aqueous acid, the ability to reduce surface and interfacial tension, and the ability to dissolve organic deposits. Also generally it is desirable for the organic liquids to be materials which will promote water wetting of sand without promoting agglomeration of the sand. Still further it is often desirable for the organic liquid to be a material which will not promote the formation or stabilization of oil and water emulsions. Other characteristics that are often of importance are the flash point and the tendency of the material to cause corrosion of metal.
One of the organic well treating agents that has often been used in the past is ethylene glycol monobutyl ether (hereinafter referred to as EGMBE). The EGMBE was found to be especially useful in lowering the surface tension of aqueous solutions and in lowering the interfacial tension between oil and water. One of the drawbacks of EGMBE has been the fact that at higher concentration it often does not form a truly miscible solution in aqueous acid. For example, U.S. Pat. No. 3,819,520 in column 2, lines 30-38 discloses that at concentrations above 10 percent EGMBE frequently does not form a clear stable solution in aqueous acid.
U.S. Pat. No. 3,819,520 also discloses that one can get clear stable acidic aqueous solutions which provide a remarkable reduction in surface tension by employing a combination of isopropyl alcohol and an octyl alcohol. The octyl alcohols alone have very low water solubility. However surprisingly, as taught by U.S. Pat. No. 3,819,520, clear stable single phase aqueous acidic solutions can be formed if octyl alcohol is employed in conjunction with a sufficient amount of a lower alcohol such as isopropyl alcohol.
An object of the present invention is to provide a multicomponent organic liquid which has advantages over either EGMBE or the octyl alcohol/lower alcohol mixture of U.S. Pat. No. 3,819,520. Still other objects, advantages, and benefits of the present invention will be apparent from the following description.